This invention relates to actuators for storage media, and particularly to read-write actuators for flat media such as magnetic disks, optical disks, and compact disks.
Disk drives and similar flat media, such as compact disks, etc., use a displaceable read head or read/write head for sensing data on the media. The displacement required is normally on the order of plus or minus 15 degrees, but can be more or less. The head is mounted on an arm which is rotatably disposed from a fixed shaft on a stationary base, thereby allowing limited rotation of the arm. The head is required to travel from the inside diameter of the disc where the innermost data resides (ID) to the outside diameter of the disc where the outermost data resides (OD) of the flat media; and the arm must move quickly with respect to the shaft in response to an input from an actuator. To obtain high speed with minimum energy, the connection from shaft to arm must allow the arm to rotate freely about a limited arc, but at the same time, changes in the arm axial orientation, called rocking, excessive arm rotation, called overswing, and vertical movement, called jumping, must be suppressed.
The above requirement for limited rotation in an actuator arm requires that there be enough resistance to motion to reduce undesired movements, such as overswing, without unduly inhibiting rotational movement. The desired resistance to excessive rotational motion is referred to herein and generally as damping. Additionally, there must be sufficient constraint in the vertical direction to movement, that is, motion parallel to the shaft axis, to prevent lifting or dropping of the arm and head, which is defined herein as jumping. Further, the actuator must retain these qualities over a relatively long lifetime, so the mechanism must tolerate wear.
The conventional mechanism provides ball bearings in spaced races around the shaft; with typically two races on the shaft. The two races, when spaced appropriately, reduce or prevent rocking. Locking the races to the shaft and to the arm, such as by the use of shoulders on the race holders or by adhesion or fastening, prevents movement parallel to the axis of the shaft, and the friction of the ball bearings in the two races provide sufficient damping. Because there is no inherent limit to the rotation allowed by the ball bearings, crash stops are included to prevent overswing, defined as rotation tending to cause the arm to take the head beyond a range defined as the space between the ID and OD discussed above.
However, the solution of the prior art is expensive and relatively subject to damage. Further, there is insufficient constraint on overswing, so damping is critical and crash blocks are required. Wear can also be a problem; for example, even a small amount of wear on the bearing races can cause rocking and jumping.
It is desired to find a solution to these and other problems with the prior art. The present design accomplishes these purposes and other desirable purposes while reducing cost and increasing reliability.
Clips, which as used herein define small, thin shear panels, with ends formed at an angle to the body of the clip whereby the clips form an open U shape, also referred to as wings. The clips are formed of flat, relatively thin pieces of a material such as spring steel, etc. This type of clip is extremely resistant to movement in the plane of the panel of material from which the clip is formed; that is, to shear forces. If the material of the panel is thin, it is very easily deformed in a direction perpendicular to the plane of the clip; that is, bending stresses normal to the shear forces. If several wings of the clips are dispersed radially around a shaft; for example, in two or more equally spaced locations, the damping, or resistance to deformation, can be made uniform around the shaft. In this way, the actuator arm can be made to rotate freely for a limited distance, with the distance being limited by deformation perpendicular to the plane of the wings of the clips, into a position where further deformation increasingly requires deformation parallel to the plane of the wings of the clips. As discussed, the wings of the clips of this embodiment of the invention are highly resistant to deformation in the plane of the panel of material forming the wings. If wings are spaced as disclosed above, in more than one location along the axis of the shaft, rocking is inhibited, as well as jumping, by resistance to deformation along the plane of the panel forming the clip and wings.
In an alternative embodiment, the clips are replaced by wings formed, for example, as part of the arm and also of the shaft, and thereby as an integral single piece. While additional tooling costs would be required, this embodiment would be more amenable to mass production techniques, since arm, shaft and wings all form a single part. Of course, the wings could also be formed as a separate assembly attached to both the arm and the shaft, or as a part of the shaft, etc. Separate clips are often desirable because they can be made of, for example, spring steel, with the arm and shaft made of another material, but with the proper materials, using integral wings could result in an overall lower cost. Other benefits of using integral wings instead of separate clips will be obvious to those using the invention.
It will be appreciated also that at or near the limits of maximum rotation the wings of the clips will have distorted from a position substantially radial to the center of the shaft to a position substantially tangent to the shaft circumference. This places the wings of the clips into a nearly planar stress, whereby maximum force is exerted. Thereby damping, due to resistance to deformation along a plane and optionally due to interference between the wings and the optional crash blocks, is also maximized. This not only reduces problems in damping, but with carefully designed wings may also allow the elimination of crash stops, which are stopping blocks formed in the arms and causing interference between the wings of the clips and the arms. A relatively long panel or wing parallel to the shaft axis will further resist jumping and rocking due to the resistance of the clip to deformation in the plane of the panels making up the wings. When made of an extremely elastic material like spring steel, wings of this embodiment of the invention are extremely resistant to wear, and provide very long lifetimes.
In the invention, a multiplicity of wings are disposed about a shaft for rotatably disposing a head or similar actuated device around a limited arc of rotation. The wings also have sufficient resistance to motion, other than rotation, to provide a stable connection between the shaft and the arm with minimal rocking, jumping, overswing or wear.